Add flag for stashable bubbles

Flag: com.android.wm.shell.enable_optional_bubble_overflow
Test: none
Bug: 341361249
Change-Id: I4b8aea74344d00331500beb3c7278c40a49d2206
diff --git a/libs/WindowManager/Shell/aconfig/multitasking.aconfig b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
index 8977d5c..66d4879 100644
--- a/libs/WindowManager/Shell/aconfig/multitasking.aconfig
+++ b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
@@ -78,3 +78,10 @@
     description: "Allow opening bubbles overflow UI without bubbles being visible"
     bug: "340337839"
 }
+
+flag {
+    name: "enable_bubble_stashing"
+    namespace: "multitasking"
+    description: "Allow the floating bubble stack to stash on the edge of the screen"
+    bug: "341361249"
+}